The disclosure of Japanese Patent Application No. 2001-143669 filed on May 14, 2002 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a collision severity determining system that operates at the time of activation of an occupant protection device, and provides a result of severity determination which can be used for adjusting, for example, the power level of deployment of the occupant protection device, such as an airbag system, thus assuring more appropriate occupant protection.
2. Description of Related Art
Occupant protection devices, such as airbag systems, which are installed on vehicles are known in the art. The timing of activation of such an occupant protection device is adjusted based on changes in the deceleration of the vehicle with time, which is detected by a deceleration sensor, or the like, incorporated in the vehicle. In order to activate the occupant protection device at a more appropriate time, it is important to detect collision of the vehicle with sufficiently high reliability. As one type of a device for detecting collision of the vehicle, Japanese Laid-Open Patent Publication No.10-152014 discloses an activation control system which includes a floor sensor disposed substantially at the center of a vehicle chassis and a front sensor or sensors disposed in a front portion of the vehicle. The control system controls activation of an occupant protection device based on decelerations detected by the floor sensor and the front sensor(s). With such an activation control system, the occupant protection device can be appropriately activated by referring to a deceleration(s) detected by the front sensor(s), even when it is difficult to detect an impact only by means of the floor sensor.
For achieving further reliable occupant protection at the time of a collision of the vehicle, it is preferable to determine severity of the collision, namely, a degree of the vehicle collision that causes a secondary collision of the occupant against an object within the passenger compartment, and adjust the level of the power for activating the occupant protection device in accordance with the collision severity. The severity determination can be made based on a deceleration detected by the floor sensor while referring to a deceleration(s) detected by the front sensor(s) as in the case where the activation of the occupant protection device is detected.
In the meantime, the vehicle is provided with a predetermined failsafe mode, so as to ensure appropriate occupant protection even when any problem occurs to the vehicle. For example, an ECU (electronic control unit) provided at a predetermined position in the vehicle monitors vehicle conditions, including those of an engine and a brake system, at regular intervals. Upon occurrence of any problem to the vehicle, the vehicle generates a certain warning or alarm, and starts operating in a predetermined fail-safe mode designed for securing the safety of the vehicle occupant.
The vehicle operates in the above-described fail-safe mode in various situations, which includes the case where a problem occurs to the front sensor or sensors. In the case of a vehicle equipped with an occupant protection device capable of determining the collision severity, results of severity determination obtained with the same output value of the floor sensor may differ depending upon the deceleration(s) detected by the front sensor(s). In view of this case, it has been proposed to program the occupant protection device in advance to use a lower threshold value than in normal cases, for determining the collision severity in the failsafe mode.
Examples of problems that can occur to the front sensor include, for example, a failure of the front sensor during normal use, which is an extremely rare occasion, breakdown of the front sensor itself due to a collision of the vehicle, disconnection of a communication line or lines around the front sensor upon a vehicle collision, and so forth. The problems arising from these different causes make it impossible to detect a deceleration from the front sensor for use in severity determination.
To ensure sufficiently high occupant protection reliability, it is preferable to determine the severity of a collision in an appropriate manner, depending upon the cause of the problem that occurs to the front sensor. As described above, the occupant protection device may be pre-programmed to use a lower threshold value upon occurrence of a problem to the front sensor, for determining the collision severity in the fail-safe mode. However, it would be more desirable to determine the collision severity depending upon the cause of the problem occurring to the front sensor, in order to achieve more appropriate occupant protection.
It is therefore an object of the invention to provide a severity determining system that is able to determine severity of a collision with improved accuracy even when a problem occurs to a front sensor or sensors.
To accomplish the above and/or other object(s), there is provided according to one aspect of the invention a collision severity determining system for determining severity of a collision of a vehicle, which system includes: (a) a first deceleration detector disposed substantially in a central portion of a body of the vehicle so as to detect a vehicle deceleration in a longitudinal direction of the vehicle, (b) a second deceleration detector disposed in a front portion of the vehicle that is located ahead of the first deceleration detector, so as to detect a deceleration at the front portion in the longitudinal direction of the vehicle, (c) a velocity change amount calculating unit that calculates a velocity change amount of the vehicle by integrating the vehicle deceleration detected by the first deceleration detector with respect to time, (d) a severity determining unit storing two or more severity determination maps defined by the vehicle deceleration detected by the first deceleration detector and the velocity change amount, each of the severity determination maps representing a threshold pattern consisting of threshold values with which the vehicle deceleration is compared so as to determine severity of the collision of the vehicle, and (e) a problem detecting unit that generates a problem detection signal that indicates that a problem has occurred to the vehicle, when detecting an absence of a signal indicative of the deceleration transmitted from the second deceleration detector. In the severity determining system, when the severity determining unit receives the problem detection signal from the problem detecting unit, the determining unit operates in a predetermined fail-safe mode for selecting an appropriate one of the two or more severity determination maps, and determines severity of the collision of the vehicle, based on the selected severity determination map.
With the collision severity determining system constructed as described above, the problem detecting unit detects an abnormality in transmission of a signal indicative of the deceleration from the second deceleration detector, and the severity determining unit operates in the fail-safe mode to determine severity of the vehicle collision. In this manner, the collision severity can be determined in a desirable manner even when a problem has occurred to the second deceleration detector.